فصلنامه پژوهش های فرسایش محیطی
سال دهم شماره 1 (پیاپی 37، بهار 1399)

Landslide as a morphological risk factor is the result of the operation of natural and environmental factors that, like other morphological irregularities, causes damage to human facilities, infrastructure, and property. One of the most significant works of geomorphology is the identification of stable landforms and places with minimal potential for catastrophic or lethal phenomena caused by environmental processes that have a detrimental effect on humans and their affinities (Rosenfeld, 2004, p. 423). Mass movements in mountainous areas are one of the natural processes and one of the most important causes of landscapes (Van Westen, 1993, p. 2) Landslide sensitivity zoning is one of the essential tools in risk management and decision making (Dahal, 2008, p 496). The purpose of this study is to identify landslide hazard zones in the downstream basins of Sanandaj Dam with an area of 970 km2. Annually, mass movements in the area cause damage to roads, power lines, rangelands and natural resources, farms and residential areas and increase the amount of soil erosion in the area. This basin is located on Sanandaj-Sirjan structural zone based on common structural divisions of Iran. Kurdistan mainly with mountainous topography, high tectonic activity, diverse geological and climatic conditions, has the major natural conditions for creating a wide range of mass movements. According to available statistics and also the research of MIRSANIE et al (2006), Kurdistan province is the third most landslide province after Mazandaran and Golestan. If it is a criterion for the ranking of the provinces, it will be ranked higher. NAIRI and KARAMI, 2018).

In this study, in order to map the landslide hazard according to geological, geomorphological, hydrological, climatic and human and environmental factors of the area, 9 effective factors include slope, slope direction, distance from fault, distance from road, distance from Waterways, lithology, land use and precipitation were identified and evaluated. The required information layers were then prepared in Arc GIS 10.6 software environment. The first step in zoning is to identify the landslides that have occurred in the area. Using the 2016 Landsat 8 ETM + satellite imagery with a spatial resolution of 30 meters, Google Earth software and field studies identified 237 landslides. In this study, 89 non-slip points were prepared for using in training and testing stages of perceptron neural network in slopes of less than 5 degrees. Artificial neural networks have been created from a number of limitations of advanced content management services to the top walkway called Neuron, which works for problem solvers and can select information through synapses. Neural networks begin to learn using the data pattern entered into them. The learning of models, which in fact determine their internal parameters, is based on the error correction law, which is the generalization of the well-known least squares method. In fact, in this method, by regularly correcting the error, the best weights that provide the most accurate output for the network are identified. The neurons fall into the input layer, the output layer, and the hidden or middle layer.

 By default, the software was selected to prevent interference and capture of the hidden layer. 70% of landslides in the study area were used to train the neural network and the remaining 30% were used as reference land data for testing and calibrating the model. Data were trained using a multilayer perceptron network with Adam's learning algorithm. In this study, a network search algorithm was used to optimize and adjust neural network meta-parameters. Because of nonlinear relationships in landslide phenomenon, relu transfer functions were used. The coefficient of learning that controls the amount of weight change is 0.01. The final network structure has 9 neurons in the input layer, 30 neurons in the hidden layer and 1 neuron in the output layer. After preparing the neural network, the study area was analyzed with 970 square kilometers with 9 input variables that were converted to raster data in 30 x 30 pixels. The results of the analysis were plotted with five categories of landslide hazard. It uses 5 methods for model error detection

The downstream area of ​​Sanandaj Dam is one of the most active areas of Kurdistan province in terms of human activities. In the risk zoning maps, the optimal areas for human activities (very low and low risk areas) as well as the unfavorable areas (high and very high-risk areas) are identified. According to the neural network model, about 31% are in the range of desirable areas for human activity. Also, about 39% are in the area of ​​undesirable and very undesirable areas. The natural features of the region affect the occurrence of landslides in the region. The results of the neural network model are in line with the realities of the region's wide-risk hazards, and high-risk areas are often located in the west and southwest of the basin. These areas correspond to the mountain unit and the steep slope. The western outskirts of Sanandaj have been affected by landslides and have been classified as high-risk and high-risk. The central and southern parts of the basin are arranged along the Qashlaq River to the exit of the basin in the areas with very low and low risk. The eastern part of the basin is affected by mass movements, especially precipitation and inflows, and is divided into areas with medium to high risk. The results of risk zoning validation show that in this region, the neural network model with 91.49% accuracy has very good accuracy. It is suggested that the resulting map be considered as a base map in order to carry out any executive actions in the area. The vastness of unfavorable areas in the basin indicates that the study area in general has a high potential for landslides.

In this century, wind erosion as one of the most important processes in arid and semi-arid regions has affected about one-sixth of the world's land area. Wind erosion is usually attributed to the process of soil particles being removed and displaced by the wind. Wind is one of the dominant processes in arid, semi-arid, and sub-arid regions and is the result of wind dynamics, transport of soil or sediment particles, and the development and evolution of desert roughness based on erosion and sedimentation intensity.The risk of wind erosion and dust is also more severe in areas where the soil is loose, dry, and bare, with high winds and high repetition. This study was conducted in Jazmourian basin and its playa. Jazmurian Playa has been studied as the most important area affected by wind erosion and the source of dust hazard in the south-east of the country; because these two hazards are often found in closed basins of old lakes or playa that contain loose sediments, and they are disconnected, they are happening.

Data used are library data, meteorological statistics, maps, field, and laboratory data. At first, using the (Eriffer) model, nine effective factors in determining the wind erosion potential in the geomorphological facies of the basin were investigated, and their sedimentation rate was determined. The annual windroses were plotted with hourly data from the synoptic stations over the period (2009-2019) for six stations, and the wind situation of the area was analyzed. Then, 20 surface sediment samples were taken from the area to determine the effect of particle size on the performance of wind processes, and Granulometry was performed. And the position of the sand-dune as the end point of wind erosion and the areas affected by the dust were also identified.

According to the results of the implementation of the Eriffer model for determining the wind erosion potential in the Jazmourian basin of high and diverse sandstone facies - very high erosion class and seasonal litter lithofacies, seasonal muddy salt marsh, terraces lakes and alluvial plain. There is a lot of erosion in the classroom. Also, alluvial facies are in middle erosion grade and uneven mountain slopes in low erosion grade. In fact, in the Jazmourian basin, there are scattered sandy masses, but the highest distribution is in the southeast of Playa, with 44.49% of sedimentation of the whole basin. The wind Baft situation in the area indicates that the maximum velocity at the station is 2.10 to 3.60 m / s. The highest wind speed at this station is in the range of 5.70 to 8.80, which accounts for about 2 percent of all winds. The Bam Station Wind in different directions at speeds below 4.5 m / s. Khash Station is about 2 percent of the winds in the speed range of 8.80-70.70, and about 80 percent is between 0.50 to 3.60 m / s. Jiroft Station is about 1 percent of the winds in the speed range of 8.80-70. Nikshahr Station At this station, about 2% of the winds blow at a speed of 5.70 to 3.70 / 60 and the Other at lower speeds. Iranshahr Station about 80% of the winds in this station are northeast to southeast and are classified at speeds of 0.50 to 3.60 m / s. Annual windrose show at stations in the area Local winds can create local dust. The results of the analysis of the samples show that 74.75% of the eastern Playa sediments, 76.25% of the southern Playa sediments, 67.50% of the northern sediments, and 95% of the Playa center sediments are below 63 microns in size. Surface sediments are the environment for the production of dust.

The results show that the low and flat topography, the presence of fine particles in the sediments, and the dominant winds during the dry season, with the dominant northwest and west direction, caused the sediment to move suspended, then jump and creep. And the dust hazard has Extensive performance on the playa and its margins, and more importantly, the Jazmourian playa is one of the main sources of dust in the south-east of the country. Also, the areas covered by dust hazards are greater in the central, southern and, western margins of the hole than in other areas.

The turbulent jets downstream of hydraulic structures, such as sluice gates, jet nozzles, spillways, or weirs, may cause severe local scour. The scouring process is inherently complex due to the rapid change of turbulent flow characteristics with sediment motion in the scour zone. Excessive scour is undesirable and may be detrimental to the foundations of the structures. Sluice gates are wood or metal sheets that slide vertically and act as a portal to regulate the water passage within the irrigation channels, dams, and some wastewater control plants. The operation of the gates in small channels is traditionally accomplished manually, while in modern channel networks or relatively large channels, an electrically or hydraulically powered mechanism should be considered. The flow passing the gate forms a high-velocity jet with a relatively  high erosive force that may develop a scour hole in an erodible channel downstream of the gate. To reduce the destructive action of the jet and regulate the flowing fluid under the gate, a rigid and non-erodible apron is commonly constructed under and downstream of the gate. In this case, the scour forms downstream of the apron, and depending on its shape and depth, it may threaten the stability of the gate foundation. In fact, the apron is generally a thin concrete layer implemented on the canal bed sediments, and its stability depends strongly on the strength of the sediment particles against detachment. The interaction between the flow and the sediment particles may extend the scour hole up to the downstream edge of the apron over a relatively short time. Afterwards, the sediment particles beneath the apron detach and wash away over a longer duration, causing to undermine the apron. Depending on the flow intensity, sediment size, and apron length,  this phenomenon may occur in a few hours to several months. A collapsed apron may interrupt the flow passage and threaten the whole structure stability.Recently, several studies have been conducted so as to improve our understanding of the phenomena of scour and sediment transport due to a horizontal jet issuing from below a sluice gate. The high-velocity jet issuing from below the gate produces shear stresses that exceed the critical shear stress for the incipient motion of the bed material. Over a period of time, the scouring of the bed material causes the flow depth downstream from the gate to increase, thereby resulting in a mechanism of reduced bed shear stress, which in turn reduces the rate of scour. Though the flow field is simple, the scour mechanism is complex and dynamic.

The dimensions and flow conditions of the numerical model were the same as Kells et all., 2001 laboratory model. The geometries of the numerical model were created using flow3D software, and solutions were created out by VOF method. In this study, the effect of grain size on the dynamics of local scour processes is discussed in the context of the erosion that takes place downstream from a submerged sluice gate. Three gradations of non-cohesive bed material were used to study the scour process for various tailwater depth and sluice openings. The sand gradations included three sizes of uniformly graded. A total of 18 model was simulated, each for a period of 2 h. An equilibrium scour condition was attained over this time period for all of the models, although a sense of similarity in the bed profiles is observed in the region close to the sluice gate.

The present results indicate that the depth and the area of scour are highly dependent on the bed grain size, both increasing as the grain size is reduced. Moreover, the maximum scour depth increases with increases in the tailwater depth.Finally, it was found that the location of the point of maximum scour depth, as measured from the upstream end of the erodible sand bed, moved downstream with an increase in either the opening or tailwater depth and upstream with an increase in the grain size.

The primary purpose of this study was to evaluate the effect of grain size and, to a lesser extent, of grain size distribution on the dynamics of local scour below a sluice gate. In short, it was found that the grain size has a significant influence on the extent of scour, which occurs, with more scour occurring for smaller-sized material. As well, it was found that less scour occurred for a graded sand than a uniform one having a similar median grain size. Of particular interest, however, is that for any given grain size, the greater is the tailwater depth, the greater is the depth, extent, and volume of scour. It appears that the tailwater serves to slow the rate of jet expansion, thus increasing the length of bed exposed to high velocity, hence high shear stress, conditions.

Addition of biochar to soil has been recently considered as an amendment to reduce soil erosion. Biochar contains pyrogenic carbon, which is produced by heating residue of various crops, woods (or in other words various biomass) in restriction or absence of oxygen. Biochar can affect soil organic matter level and aggregate stability. Reduction of soil erosion through maintenance and  the increase of organic matter, increase of aggregate stability and improvement of hydraulic conductivity, and enhancement of moisture retention as a result of biochar application should be considered as an important achievement. It is important to study the effect of the different methods of biochar addition to the soil. The method of uniformly mixing biochar with surface soil which has been used in most studies can disturb the natural structure and lead to soil degradation. Therefore, it is an important issue to introduce a practical method that is associated with minimal soil manipulation, especially in erosion-prone soils. The effect of the biochar addition as suspension in water has never been reported in previous studies. Therefore, the aim of this study was to investigate the effects of adding different levels of biochar produced from two types of feedstocks (horticulture and agriculture wastes) in form of aqueous suspension on the properties of two types of erosion-prone soils in southern Guilan.

Two erosion-prone soils which were undisturbed, were sampled by metal cylenders (diameter and height of 25 and15 cm, respectively) of marl lands located in southern guilan. These soils were named as SL and L. Texture of SL and L were sandy loam and loam, respectively. Two types of biochar were produced from different feedstocks including pruned branches of ash tree (Fraxinus excelsior) and rice husk by slow pyrolysis at a temperature of 550 °C in a muffle furnace, titled as WB and RB respectively. The yield of biochar was determined based on weight of biochar produced per unit weight of raw material. The amount of ash in the biochar was determined by heating five grams of biochar at 500 °C for more than 8 hours and weighing it again. The pH and electrical conductivity were measured in a mixture of biochar and deionized water with a weight ratio of 1: 20 (biochar: water). The total amount of carbon, hydrogen, and nitrogen in biochars was determined by dry combustion. Two types of produced biochars were milled with a particle size of 63-250 microns, at levels of 0.7 and 1.4% by weight. Three repetitions in the form of aqueous suspensions were added to the cylinders containing undisturbed soil. Three cylinders of soil without biochar were also considered as control treatment. Soil cylinders were placed in a greenhouse for six months at a temperature range of 20-25°C and underwent several cycles of drying and wetting. At the end of incubation period, soil samples were obtained from cylinders. Soil properties including pH, electrical conductivity, organic carbon, hydraulic conductivity and aggregate stability were also measured. Thin sections were also taken out of soils and state of soil structure and voids were studied. The effect of two factors, including biochar type and biochar application level were analyzed as factorial in a completely randomized design by SAS statistical software. The comparison of the means was done by Duncan's test at the probability level of five percent.

The WB compared to RB, had a higher yield, and less ash content, pH, electrical conductivity and H/C and O/C. More mineral ash in biochar is likely to provide more electrical conductivity in RB. Both biochar had an alkaline pH (more than 7). The biochar used in previous studies were usually alkaline, but biochar can be produced with any pH in the range of 4 to 12. The raw biomass has a H/C  molar ratio of about 1.5, but with the pyrolysis, this ratio decreases. WB had less H/C compared to RB. Therefore, it can be concluded that WB had more aromatic carbon and it can probably be a more effective tool for carbon sequestration in soil. Presence of a lot of pores in biochar, especially WB which were visible in SEM photos, are very effective on vital soil functions such as aeration and hydrology. The organic carbon content of SL and L soils were significantly higher at biochar treatments compared to control. The hydraulic conductivity of SL soil at both application levels of WB and RB was significantly lower than the control. However, both application levels of WB and 1.4% of RB led to significant increase and decreases of hydraulic conductivity of L soil, respectively. The mean comparison showed no difference between bulk density of treatments and application levels of biochar to control treatment of SL soil. However, Bulk density of biochar treated L soils were less than control. Biochar treatment also result in significant increase of: mean weight and geometric mean diameter and decrease of fractal dimension of aggregates in L Soil.

WB and RB biochars had no significant effects on indexes of soil aggregate stability and bulk density of SL soil, but they led to significant improvement of bulk density and aggregate stability of L Soil. Although, assessment of thin section showed partial improvement of soil structure of both SL and L soils. Therefore, more time than 6 months of incubation probably is needed to significant improve of aggregate stability of SL. Application of both biochars led to increase of organic carbon of both SL and L soils. Hydraulic conductivity was decreased in SL soil as result of both biochar application which can lead to the increase of water retention. Although the increase of hydraulic conductivity of  L soils due to WB can be considered as a suitable approach for the decrease of  the runoff, Generally, it can be concluded that due to the significant effect of feedstock type on biochar characteristics and different characteristics of soils, various types of biochar do not have a similar effect on a particular soil, therefore, a type of biochar cannot have the same effect on different types of soil.

 The quality of soil physically, hydraulically, and mechanically are not similar in various land uses, slope aspects and positions in the steep lands. There is extensive information around the world about the land use effects and how to lessen the extent of the slope position effects on soil properties. Although several studies have been conducted regarding the land use effects on various soil mechanical properties, little is known about the effects of land use and slope positions on the shear strength and penetration resistance. The objective of this study was to compare some soil quality parameters in different land uses, slope aspects and slope positions in the steep lands of Heyran Neck, Ardabil Province, Iran.

The study was conducted in the Heyran Neck, Ardabil Province located at the 40 km of Ardabil-Astara road, northwest of Iran (48° 36ʹ 7ʺ E and 38° 23ʹ 37ʺ N). The factorial experiment was carried out based on completely randomized design with four replicates. The first factor was two land uses (forest and rangeland), the second factor was two slope aspects (north and south) and the third factor was three slope positions (shoulder, footslope, toeslope). Totally, 48 disturbed and undisturbed (using steel cylinders with 5 cm diameter and height) samples were taken from 0-10 cm soil depth. Sand, silt and clay (hydrometer method), organic carbon (Walkley–Black method), bulk density (cylinder method), saturated water content (gravimetric method), field capacity water content (equivalent 30 kPa suction) and permanent wilting point water content (equivalent 1500 kPa suction) using pressure plates method were measured in the collected soil samples. A shear vane was used to make shear strength measurements in saturation condition. The procedure used in this study was pushing the vane into the soil surface until the blades were covered (about 8 mm depth); a clockwise rotation rate was then applied to ensure that failure developed within 5 to 10 sec. The maximum stress value was recorded on a dial at the top of the vane driver. Vanes with a stress range between 0 and 100 kPa were used in all cases to induce shear failure. A non-return pointer assisted in readings. Penetration resistance was measured in the undisturbed soil samples (steel cylinders) using automatic micro penetrometer equipment (with three replicates) in the water content equivalent 1 bar suction. Data’s normality was assessed through Kolmogorov–Smirnov test; also, the analysis of variance and comparison of means by Duncan test and Pearson correlations were done using SPSS software. Figures were prepared using Excel software.         

The textural classes of studied soils were sandy loam (n= 8), loam (n= 10) and clay loam (n= 6) in the forest land and clay loam (n= 16), loam (n= 6) silty clay loam (n=1) and clay (n= 1) in the rangeland according to American textural triangle. There were found significant correlations between soil organic carbon and shear strength (r= 0.74**), bulk density (r= -0.59**), penetration resistance (r= -0.30*), saturated (r= 0.58**), field capacity (r= 0.42**) and permanent wilting point (r= 0.37**) water contents. Shear strength significantly correlated with clay (r= 0.35*), bulk density (r= -0.59**) and penetration resistance (r= -0.33*). The mean values of organic carbon, sand, saturated and permanent wilting point water contents in forest lands were significantly higher than range lands. The mean values of clay, bulk density, penetration resistance and field capacity water content in range lands were significantly higher than forest lands. The mean values of organic carbon, silt, clay, shear strength, saturated, field capacity and permanent wilting point water contents in northern slope were significantly higher than southern slope. The mean values of sand, bulk density and penetration resistance in southern slope were significantly higher than northern slope. The highest value of bulk density (1.46 g/cm3) was found in southern aspect and toeslope position. The highest values of field capacity (30.45 % g/g) and permanent wilting point (20.83 % g/g) water contents were found in shoulder position and had significant difference with footslope and toeslope positions.

In general, the results showed that from forest land use to rangeland in Heyran Neck of Ardabil Province, The quality of soil physically, hydraulically, and mechanically were reduced. Also, soil quality of northern aspect was higher than southern aspect because of intensive plant cover and high soil moisture. Soil quality of toeslope was less than shoulder and footslope position in the studied region.

Soil erosion is one of the most important environmental issues that causes various ecological, social and economic problems. Today, the use of various models for estimating and predicting hydrological data of watersheds is increasing. Soil erosion risk assessment is a special form of land resources evaluation, and its purpose is to divide the land into small areas based on the type of erosion and its amount, which is essential in the soil conservation planning. Developing comprehensive soil erosion models applicable in different environmental conditions is highly important. The Intensity of Erosion and Outflow (IntErO) model is a new graphical model that has a user-friendly software and could present a comprehensive view from watershed erosional components. Awareness of important coefficients such as watershed development, river basin tortuousness, erosion energy of the basin's relief, the region's permeability, vegetation cover, and deposit retention coefficients that provided by IntErO model has a key role to adapt proper watershed management and conservative measures, particularly the best management practices (BMPs) that are currently considered by policymakers and executive managers.

Due to the positive reports on the proper efficiency of the IntErO model in some parts of the areas such as Bosnia & Herzegovina, Bulgaria, Croatia, Czech Republic, Italy, Brazil, and recently in North Khorasan and Kurdistan provinces, the present study was conducted with the aim of obtaining comprehensive information on the erosional characteristics of the KoozehTopraghi Watershed located in the southern part of Ardabil Province. The studied watershed with an area of 801.40 km2 was divided into 36 sub-watersheds according to topographical and hydrological properties. Totally, the IntErO program package for estimating soil erosion and sediment yield components uses 26 input data including geometric, topographic, maximum outflow, hydrological and soil erosion intensity properties. All primary maps for total watershed and its 36 sub-watersheds were processed and provided in the ArcGIS 10.6 environment. Then, according to the required standards of the model, the data bank was provided in the Excel 2016 environment and accordingly uploaded to the IntErO software. Finally, after running the IntErO model, 22 components related to the soil erosion process of KoozehTopraghi Watershed were obtained.

According to the results of the IntErO model, the spatial variability was confirmed in relation to the most of erosional components through 36 sub-watersheds which indicate the diversity of ecological and biophysical conditions at the whole watershed. In general, the maximum and minimum ​​of soil erosion coefficient (Z) were estimated in the sub-watersheds 6 and 10, respectively. According to the obtained results, most of the study sub-watersheds have experienced severe erosion. It was also found that the mean of the production of erosion material in the river basin (Wgod) was equal to 222854.65 m3 y-1, respectively whereby it’s minimum and maximum were obtained in the sub-watersheds 6 and 33, respectively. The reason for the high amount of specific sediment yield in some sub-watersheds can be attributed to their severe exploitation for human needs and consequently severe erosion. The results also showed that the mean value and standard deviation of the coefficient of the deposit retention (Ru) for the whole watershed was 0.26 ± 0.09. The values ​​of real soil loss (Ggod) and specific real soil loss (Ggod/km2) were evaluated as 172704.90 m3 y-1 and 215.50 m3 km2 y-1. The results showed that there was a lot of permeability in the upland sub-watersheds. In these sub-watersheds, due to the existence of rangelands and higher vegetation cover, more water penetrates.

In general, the results showed that the erosion values ​​at the lowlands of the study watershed are much higher than at the highlands. The present results are consistent with the other researches that reported the high level of ecological sensitivity in the lowlands of ​​the KoozehTopraghi Watershed. The results of the present study can be used as a useful managerial tool in the field of sustainable agricultural production and optimal use of natural resources. Finally, it is recommended to compare the applicability of the IntErO model in different environmental conditions, considering its comprehensiveness in analyzing the erosional status. The results of this study, in addition to its capability for modeling different watershed ecological, hydrological and managerial processes, their analysis is useful to prioritize the critical regions as well as sustainable and effective implantation of restoration and conservative practices in the KoozehTopraghi Watershed.